arch: arm: soc: stm32f4xx: Add LL include file also for I2S case

stm32f4xx_ll_spi.h include file is shared between I2S and SPI
(controller is same). So we need to include it even when I2S_STM32
is enabled.

Signed-off-by: Armando Visconti <armando.visconti@st.com>